Banknote imaging

Abstract

A method of obtaining a plurality of infrared images of a banknote that involves simultaneously illuminating the banknote with infrared light at a first wavelength and infrared light at a second wavelength, capturing an image of the banknote with an RGB camera, obtaining from both a first output channel signal and a second output channel signal of the RGB camera sensor where the intensity distribution of the infrared light at the first wavelength and the intensity distribution of the infrared light at the second wavelength uses a first calibration coefficient and a second calibration coefficient of the RGB camera sensor, producing separate infrared images of the banknote at the first wavelength and the second wavelength from the respective intensity distributions.

The invention claimed is: 
     
       1. A method of obtaining a plurality of infrared images of a banknote comprising:
 simultaneously illuminating the banknote with infrared light at a first wavelength and infrared light at a second wavelength, wherein the first and second wavelengths are different, and wherein the first wavelength is between 400 nm and 1000 nm, and wherein the second wavelength is between 400 nm and 1000 nm; 
 capturing an image of the banknote with an RGB camera; 
 obtaining from both a first output channel signal and a second output channel signal of the RGB camera sensor an intensity distribution of the light at the first wavelength and an intensity distribution of the light at the second wavelength using a first calibration coefficient and a second calibration coefficient of the RGB camera sensor; and 
 producing separate infrared images of the banknote at the first wavelength and the second wavelength from the respective intensity distributions; 
 wherein the first calibration coefficient is defined as a ratio of the first output channel signal amplitude at the light first wavelength to the second output channel signal amplitude at the light first wavelength; and wherein the second calibration coefficient is defined as a ratio of the second output channel signal amplitude at the light second wavelength to the first output channel signal amplitude at the light second wavelength; and 
 wherein a first output channel includes a first output channel of the RGB camera sensor, and wherein a second output channel includes a second output channel of the RGB camera sensor, wherein the first and second output channels of the RGB camera sensor are different channels of the RGB camera sensor. 
 
     
     
       2. A method of  claim 1 , wherein the RGB camera sensor is a CMOS or CCD image sensor. 
     
     
       3. A method of  claim 1 , wherein the RGB camera sensor includes a Bayer filter matrix. 
     
     
       4. A method of  claim 1 , wherein the first wavelength is 730 nm and the second wavelength is 880 nm. 
     
     
       5. A method of  claim 1 , wherein the first and second wavelengths are emitted from a first infrared LED and a second infrared LED respectively.